In digital communication systems, audio data, video data or other user data is usually transmitted in coded format. Provision is often made for compressing, by means of real-time or quasi-real-time coding methods, the user data that must be transmitted. In this case, it is usually preferable as far as possible to reduce the volume of data that must be transmitted, and hence a transmission rate, without overly compromising a subjective auditory impression in the case of audio transmissions, for example.
In particular, two classes of coding methods are known for coding audio and voice signals. The first relates to coding methods which act in the time domain, wherein a curve shape of the audio signal is coded or decoded with reference to the time, and the second relates to coding methods which act in the frequency domain, wherein a frequency-response characteristic of the audio signal is coded or decoded. Examples of coding methods in the time domain are the so-called CELP coding methods (Code Excited Linear Prediction). One example of a coding method in the frequency domain is the so-called AAC method (AAC: Advanced Audio Coding) of the Moving Picture Expert Group (MPEG), which uses a modified discrete cosine transformation. A further example of a coding method in the frequency domain is the so-called TDAC method (Time Domain Aliasing Cancellation).
Coding methods in the time domain are often known as “time domain coding” and coding methods in the frequency domain are often known as “frequency domain coding” or “transform coding”.
The so-called “overlap-add method” is frequently used in frequency domain coding methods, whereby the user data from consecutive data packets is added using a predefined overlap.
In this context and in the following, data packets are understood to mean both data packets in the sense of a packet-oriented transmission, e.g. IP packets (IP: Internet Protocol), and so-called data frames.